Friday, April 6, 2012

Post-savanna burn observations

Our large savanna burn of 29 March was a major success, resulting in over 30 acres burned. The coverage was close to 100%, which is quite an improvement from our experience a few years ago. The view here, in the midst of what we call the Basin Savanna, was taken two days after the burn.

We have a definite philosophy about mop-up. We only put out smokers if they have the potential for being a hazard. Because of the large size of our burns, we have very little edge effect. When we did the 29 March burn, all of the land on all sides of the savanna had already been burned and was black. We let flaming logs that are on the ground burn up.

The photo below shows what happened to a large hickory that had toppled last winter. It caught on fire during the burn and although it rained a few hours after the burn was completed, the logs were still burning the next day. They continued to burn and in fact are still burning at this moment. The upper photo below was taken a week after the burn and lower one three days later. You can see the gradually lengthening gray ash which shows the outline of where the logs burned. In the second photo, the ash layer is about 12 feet longer.These logs are burning only at the end, the fire gradually eating into the log. We could easily put them out, but since they are surrounded by a vast area of black, it is preferable to let them burn.

These photos also provide a good view of the Basin Savanna. The oaks on top of the ridge are mostly burs and those lower down are whites.

How often should an oak savanna be burned? There is extensive data from the research at Cedar Creek Natural Area in Minnesota. The results indicate that frequent burns are desirable. This agrees with work done in Iowa at Timberhill Savanna, and in Wisconsin by Rich Henderson.

Mark Leach, who has done extensive research on the ecology of Wisconsin savannas, states what he calls "the four essential ingredients for restoring a degraded oak savanna:

"1. Decrease the abundance of non-oak trees and shrubs (and get more light to the groundlayer). I call this restoring the vertical structure.

2. Control or eliminate pest plants.

3. Burn annually, at least for five to 10 years, and then burn as needed on an irregular pattern.

4. Add species, if and where needed."

At Pleasant Valley Conservancy, because of our long legacy of buckthorn and other invasive shrubs, we plan to burn annually into the foreseeable future.